arm64/smp: Remove unused irq variable in arch_show_interrupts()

    arch/arm64/kernel/smp.c: In function ‘arch_show_interrupts’:
    arch/arm64/kernel/smp.c:808:16: warning: unused variable ‘irq’ [-Wunused-variable]
      808 |   unsigned int irq = irq_desc_get_irq(ipi_desc[i]);
	  |                ^~~

The removal of the last user forgot to remove the variable.

Fixes: 5089bc51

 ("arm64/smp: Use irq_desc_kstat_cpu() in arch_show_interrupts()")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201215103026.2872532-1-geert+renesas@glider.be
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>